Almost 1,000 police officers from England and Scotland are to begin training for deployment in Northern Ireland in case of disorder from a no-deal Brexit, the Guardian has learned.

The plans were put in place after Police Service of Northern Ireland (PSNI) chiefs asked for reinforcements to deal with any trouble that arises from a hard border. The news came on a day of growing concern that a no-deal Brexit is becoming a distinct possibility.

The Irish prime minister, Leo Varadkar, said Ireland was "now preparing for no deal with the same level of seriousness that we would" Theresa May's deal, adding that he and the German chancellor, Angela Merkel, had spoken and agreed that there could be no change in the offer to the UK.

EU leaders rebuffed May's hopes that her round of phone diplomacy could prompt any movement, saying "negotiations have concluded".

May's attempts to woo the Democratic Unionist party were again rejected after two days of intense negotiations, making the chance of victory for the prime minister in the crucial mid-January vote on her deal still more remote.

The prospect of large numbers of English and Scottish officers being deployed on the streets of Northern Ireland after 29 March could anger republicans and complicate efforts to restore the power-sharing executive at Stormont, which collapsed in 2017.